Kevin Anderson upset third seed Andy Murray at the U.S. Open in a dramatic four-set match to reach his first major quarterfinal. Stan Wawrinka and Victoria Azarenka defeated Americans Varvara Lepchenko and Donald Young to secure spots in the quarterfinals.

Three of the four sets went into a tiebreak, but it was easy to see Murray quickly faded towards the end. Sports Illustrated reported a head cold bogged him down during the tournament. Anderson won the tiebreak in the first set with a mini-break and completely dominated the second set. However, some life remained in Murray in the third set when he led off with a break. Anderson powered back and demolished Murray in the tiebreak. The Brit found a way back with both players preserving their serves in the fourth, but it was too much. Anderson won the tiebreak 7-0.

Azarenka, seeded 20 in the tournament, easily routed American Varvara Lepchenko in straight sets. The former world number one and two-time Australian Open champion is finally coming back to her former self. She missed the majority of 2014 due to injuries. Her play on Monday showed she deserves higher than a 20 seed. A true test will occur in a match between second seed Simona Halep, who defeated Sabine Lisicki in three sets. Halep showed signs of fatigue and pain as she fought hard against the German. But Lisicki ran out of steam as the Romanian rolled over her in the third set.

French Open champion Stan Wawrinka ended American Donald Young’s run at the tournament in four sets. Young twice came back after being down two sets to keep advancing. Young took advantage of an error-filled second set against Wawrinka, but the fifth seed fought back and wiped out Young in the next two sets.

On Tuesday, Roberta Vinci will start the day against Kristina Mladenovic. Roberta Vinci walked over to the quarterfinals after Canadian Eugenie Bouchard fell in the locker room. Doctors diagnosed her with a concussion, which forced her to withdraw. Bouchard wanted an ice bath after her mixed doubles match with Nick Kyrgios. The locker room was dark and she slipped on water, “falling backward and landing on the back of her head.” After them, Jo-Wilfried Tsonga will play against defending champion Marin Cilic.

World number one Novak Djokovic will close out the night against Feliciano Lopez, but the talk of the night will be the matchup between the Williams sisters right before them.

Serena is only three wins away from achieving a calendar Grand Slam, but she must defeat older sister Venus. The powerhouse duo met at Wimbledon, with Serena emerging victorious. The number-one player in the world is the favorite, but matches between the sisters are always fascinating considering they are best friends and a few of the most talented tennis players to ever grace the sport. Venus is showing sparks of her old self as she only dropped two sets in the entire tournament, both in tiebreaks. She easily won all the other sets. If there was a time for Venus to defeat Serena this could be it.